In a conventional mechanism, a balance staff carries a balance fixed via a hub of the balance felloe, and held bearing on a surface of a first side of a median seat of the balance staff. On this first side, beyond the hub, a collet fitted onto the staff in proximity to a first end thereof forms the moveable point of attachment of a balance spring which is also attached to a plate or bar. On the second side of the balance staff, opposite the side carrying the collet, the staff carries, away from the median seat, first of all a large roller carrying an impulse pin which cooperates with the pallet fork, then a small roller with a notch cooperating with a dart of the same pallet lever to prevent any accidental movements of the fork.
The safety devices should be of sufficient size in the transverse direction of the movement, i.e. parallel to the pivot axes of the balance and of the pallets. Particular attention must be given to the safety device between the surface of the large roller facing the pallets and the corresponding surface of the lever which carries the horns delimiting the pallet fork. The same applies between the end of the impulse pin, also called the roller pin, and the surface of the dart facing said pin. The same attention must be given to the safety device between the other surface of the dart and the plate carrying the combined unit.
In numerous movements, the pallet/balance settings are insufficient, which causes a risk of collision, and these settings are in general out of balance.
It is clear that making these safety devices too large is detrimental to the total thickness of the movement, the section of whose components is constant?.
A compromise must therefore be found between operating safety, to prevent any risk of collision, and the total thickness of the movement.
It is not always easy to move components in order to provide safety devices, because of the presence of various bridges, the balance felloe, and other mechanisms with which there is a risk of interference, for example the date discs, which form a barrier preventing stones or incablocs from being moved to provide for security devices, particularly because of the safety device required between the balance felloe and the oscillating weight, which is provided by platforms in a fixed position, and which prevent the balance felloe being moved axially.
Further, the conventional solution is to provide adequate safety devices and settings, to the detriment of the thickness of the movement.
U.S. Patent No. 2010/157743 in the name of Roger Dubuis discloses a particular method of fixing the balance spring to the collet by matching a balance spring to a balance, and the assembly of the balance spring on the balance with a collet selected from among a collection of collets suited to different attachment distances of the inner coil relative to the staff. The balance thus includes a removable collet for attaching the balance spring. This balance includes a median seat, on each side of which are held bearing, on a first side, the balance beyond which a collet is driven in, and on a second side, a sleeve with the two rollers and the impulse pin.
CH Patent No 270582A in the name of Brendler discloses a conical balance staff onto which is fitted a first sleeve which carries, on a first side, a balance which bears on a first surface of the first sleeve forming a first seat and is immobilised by a first sharp rivet edge on the first end side of the staff, said first sharp rivet edge forming a second seat on which a collet is held bearing, the collet being immobilised by a sharp rivet edge at the first end of the first sleeve. The first sleeve also carries, on a second side, a second sleeve, which bears on a second surface of the first sleeve and carries balance rollers and is immobilised by a sharp rivet edge on the second end side of the first sleeve and corresponds to the second end of the balance staff.
FR Patent Application No. 1216100 A in the name of Pizon discloses several balance embodiments. In a first embodiment, a balance includes, on either side of a seat, on a first side, the balance supported on one surface and immobilised by the collet driven onto the staff, and on a second side a double roller mounted on a conical shoulder of the staff. The other embodiments include a sleeve with a single-piece double roller with a seat for the balance supported on one surface of the seat on the opposite side to the rollers, the collet abuts on a surface of the sleeve without any contact with the balance, and is mounted, depending upon the case, directly on the sleeve or on a threaded arbour on which the sleeve is mounted.
CH Patent No 95065 in the name of Koehn discloses a balance including, mounted on a smooth staff with a single shoulder, a sleeve including, beyond the two rollers, a balance-seat immobilised by a sharp rivet edge on the opposite side to the rollers, the collet being driven further onto the sleeve.
CH Patent No 474101 in the name of Fabriques de Balanciers Réunies discloses, a sleeve including a double roller, which is fitted onto a smooth staff, wherein the large roller with the impulse pin is also used as a direct support for the balance, which is immobilised on the opposite side by the collet driven onto the sleeve.
GB Patent No 831161 in the name of Smith, discloses a single-piece balance, with the pin and the notch on a first side of the felloe, and an off-centre collet on the other side of the felloe.
DE Patent No 2427021 SA1 in the name of Ebauches Bettlach discloses a balance staff including a seat with the notch, the balance felloe is supported on a surface of the seat and carries the impulse pin, the balance is held by the collet driven onto the staff.
U.S. Pat. No. 1,423,480, in the name of Needy, discloses several balance embodiments. In a first embodiment, a staff including a conical shoulder carries a first sleeve on which the balance is supported on an opposite side surface to the collet which is supported on said first sleeve, the first sleeve is held on the locally threaded conical staff by a nut in a recess in the first sleeve; and a second sleeve with a double roller and impulse pin is fitted onto a shoulder of the staff beyond the first sleeve. The other embodiment includes a ring screwed onto the staff underneath the first sleeve to hold the latter.
CH Patent Application No 700260 A2 in the name of Cartier discloses a single-piece staff with a median seat, on a first side of which the balance felloe bears, and beyond, the collet is fitted onto another shoulder, the seat forming the large roller carrying the impulse pin and the staff including the small roller on the second side opposite the balance.